Artificial stones well known in the art are produced by mixing crushed naturally occurring stones with resin and solidifying the resulting product. Further, various improvements have been made to these artificial stones in order to obtain products having the appearance like a naturally occurring stone such as a marble, a granitic stone, etc., and yet having excellent hardness and strength
As an attempt to improve the function and performance of the artificial stones above, there is proposed to impart alight-emitting function by using a luminescent or fluorescent substance or a light-emitting substance such as a light-storing material. As such attempts, there is proposed a method comprising solidifying a mixture obtained by mixing a phosphorescent substance with a resin component which is used as the binder of an artificial stone, or a method comprising constituting the artificial stone by mixing a light-storing fluorescent substance or an ultraviolet fluorescent substance, e.g., strontium aluminate, with an unsaturated polyester, a methacrylic resin, a glass, etc., and after solidifying the resulting mixture, crushing it to provide aggregates for the artificial stone.
However, the luminescent or fluorescent artificial stones known heretofore obtained by either of the methods above are based on the phosphorescent function of tie light-storing materials and the like, and are yet to be improved in initial brightness or in the durability of the brightness. From the viewpoint of practical disaster prevention, it has been demanded an artificial stone still improved in luminance and having a longer lasting luminance.
In the conventional artificial stones, moreover, the effective phosphorescent function was available only from the exposed surface portions of the resin components or the aggregates, and not from the light-storing materials or the fluorescent substance incorporated inside the molding of the artificial stone. However, a fluorescent substance such as a light-storing material and the like are extremely expensive, and even a small amount of addition of such fluorescent substance greatly increases the product cost of the artificial stone by about three to ten times. Accordingly, such conventional artificial stones produced by internally incorporating the fluorescent substance were costly, and thereby practically unfeasible.
Thus, it has been considered conventionally to provide a light-emitting layer only on the surface portion of the molded artificial stone, or only to the guiding figures or patterns; however, the local allocation of the light-storing material and the like further makes it difficult to improve the brightness and the durability of the brightness. Moreover, since the light-emitting layer of a conventional type is inferior in adhesive strength with the base material and is poor in resistance against abrasion, it has been found to suffer problems of not exhibiting the desired function, particularly when used in floorings, due to the separation, peeling off, wear, etc., of the light-emitting layer.
Accordingly, even in case the light-storing substance is used only for the figures and patterns, there was still a demand of realizing a novel type of artificial stone still excellent in its phosphorescent luminance and durability of the luminance, and yet improved in adhesiveness and integration with the base material of the light-emitting layer and in mechanical properties such as the resistance against abrasion, etc., suitable for use as, for instance, a light guide under a dark field environment or an ornamental material in night time.